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LOAN COMMITMENTS AND OTHER RELATED ACTIVITIES - Additional Information (Detail) - USD ($)
 3 Months Ended 12 Months Ended 32 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2018
Mar. 31, 2019
Other Commitments [Line Items]          
Commitments to make loans, period, maximum 30 days        
Affordable Housing Fund Investment          
Other Commitments [Line Items]          
Alternative investments unfunded investment commitments $ 11,100,000       $ 11,100,000
Small Business Investment Companies          
Other Commitments [Line Items]          
Alternative investments unfunded investment commitments 8,600,000       8,600,000
Other Investments          
Other Commitments [Line Items]          
Alternative investments unfunded investment commitments 500,000       500,000
Los Angeles Football Club (LAFC) Naming Rights, Revenue Rights, And Other Sponsorship Rights          
Other Commitments [Line Items]          
Maximum commitment 100,000,000 $ 100,000,000   $ 100,000,000 100,000,000
Related party term of contract   15 years      
Advertising and promotion expense 1,700,000 $ 1,700,000      
Payments for naming rights 1,400,000   $ 10,000,000 $ 5,300,000 16,700,000
Prepaid commitment balance, net of amortization $ 8,400,000       $ 8,400,000